The invention relates to a semiconductor element, in particular for switching an electrical connection.
Such elements are used in automotive engineering, for example, for the all-electronic switching of the onboard vehicle electrical supply. In the event of overloading, the semiconductor switches used can break down and thereby change over to an undefined low-impedance state. The semiconductor switches and, if appropriate, also connected devices and electronic circuits may thereupon exhibit malfunctions, be overheated and catch fire.
Existing fusible links cannot definitely help in the case described, since the currents necessary for them to effect disconnection are not achieved in every fault situation. Moreover, overcurrent cutoffs integrated in the semiconductor can only function as long as the semiconductor chip itself still functions entirely satisfactorily, which likewise cannot, in practice, be guaranteed for all fault situations.
The object of the present invention, therefore, is to specify a semiconductor element which is protected against the possible consequences of overloading. The intention is for the element to be able to be produced simply and inexpensively in large numbers.
This object is achieved according to the invention by virtue of the fact that a substance which expands to a great extent when heated is arranged on the element in such a way that if the element is overheated, the electrical leads of the element are disconnected by the expanding substance. In the event of overloading, a semiconductor element according to the invention is heated up to an increasing extent on account of its finite electrical resistance. The invention utilizes this overheating for triggering the protection element. The electrical leads to the element are severed, preferably torn off, by suitably arranged portions of the substance. Furthermore, due to the resulting pressure of the expanding substance, structural parts can be driven apart and utilized for interrupting the electrical connection.
A first refinement of the invention provides for the substance to be a substance which vaporizes rapidly at a predetermined limit temperature.
A further refinement of the invention provides for the substance to be a substance which swells up at a predetermined limit temperature.
Another refinement of the invention provides for the substance to expand explosively when a predetermined limit temperature is exceeded, and the substance to be arranged in such a way that the leads are disconnected on account of the explosion. A pyrotechnic material, similar to that used in airbags, can be used for this purpose.
Effective interruption of the electrical leads can be achieved by the substance being arranged between the semiconductor element and a further part in such a way that the further part and the semiconductor element are driven apart by the expanding substance, and the leads provided on the semiconductor element being routed in such a way that they are torn off by the further part that moves away. In this case, it may be provided, in particular, that the semiconductor element is coated with a layer of the substance, that said layer is covered by the further part, and that the leads provided on the element run through the layer and are fixedly connected to the further part. In this case, the further part may be a covering layer made of plastic into which the lead wires are cast. As a result of the increase in the volume of the substance, the covering layer is lifted from the semiconductor element and the lead wires are torn off.
A different solution to the problem can be achieved by the electrical connection to the element being effected by means of a conductive material with a low melting point, which material is arranged on the element in such a way that the connection is severed by the melting of the material if the element is overheated. In this case, the heat is supplied from the overheated semiconductor element itself. A conventional fusible link cannot be used for this purpose since the currents that occur do not exceed the current intensities that usually crop up in the system.
Exemplary embodiments of the invention are illustrated in the drawing using a number of figures and are explained in more detail in the description below. In the figures of the drawings.